A multicell radio LAN installation based on Slow Frequency Hopping Spread Spectrum signalling may consist of a set of base stations with overlapping coverage areas. In a Frequency-Hopping (FH) system, the carrier frequency of the transmitter changes at intervals of time, remaining constant between those instants. The period of constant frequency is called a "hop" and it is during these hops that messages may be exchanged. In a Slow Frequency Hopping system, the duration of a hop is at least an order of magnitude longer than typical message transmission time. A multicell radio LAN may also be referred to as a Logical LAN. Key to the successful operation of Logical LANs are effective methods for the control of interference.
There are a number of patents in this general technological area, each having certain advantages and disadvantages.
U.K. patent application GB 2,203,314A to Heading discloses a frequency hopping assignment arrangement having a processor in which is stored terrain data, radio performance data and hopper performance data. The processor is provided with a keyboard whereby geographical input information, information relating to the nets and the assignment requirements are entered. The processor is arranged to execute an algorithm in which the stored data and the information input by the input means causes the frequency hopping arrangement to assign the hopping frequencies.
U.S. Pat. No. 4,872,205 to Smith discloses a frequency-hopping communication system that when initially enabled, it detects another system operating within range by listening for a predefined radio frequency of a fixed duration. When that particular frequency is detected, the system knows that a master system is operating within range and is utilizing a first predetermined group of communication frequencies and, consequently, selects a second, third, etc. predetermined group of communication frequencies. If the particular radio frequency is not detected, the system becomes the master system, selects the first predetermined group of communication frequencies for intrasystem communication and begins transmitting the predefined radio frequency to indicate its master status.
U.S. Pat. No. 4,850,036 to Smith discloses a frequency-hopping radio communication system comprising a control unit which transmits to and receives from each of a plurality of slave stations using a frequency-hopping mode of operation. During a start-up mode, the control unit communicates a starting message to each slave station using a predefined frequency. The message identifies to each slave station a frequency-hopping sequence to be used to select the frequencies from a group of frequencies for transmission to and reception from the control unit. This message also specifies to each slave station unique starting frequencies in the frequency-hopping sequence at which to begin transmitting and receiving. All slave station transmissions are synchronized to the control unit transmissions, thereby preventing any two stations from concurrently using the same frequencies for either transmitting to or receiving from the control unit.
U.S. Pat. No. 4,998,290 to Olenick et al discloses a system for effecting radio communication over a given range of frequency channels among a plurality of participating local stations and which includes: a variably settable channel transmission unit at each such participating local station; and a controller or central station having an interference array processor for receiving data characterizing the system and each such participating local station for assigning datum channels (frequencies) to each such participating station with prescribed channel spacing and what is termed a "book-page generator" for compiling data in successive book pages of initial and subsequent channel assignments for stations with maintenance of such datum channel spacing. Further data compilations are made from the book-page generator in what are termed "station pages", comprising frequency shift instructions specific to the stations. Since a station page is derived from plural book pages, any station may be compromised without revelation of the contents of the book pages.
U.S. Pat. No. 4,554,668 to Deman et al discloses a radio communications system comprising at least one master station and a plurality of slave stations in two-way frequency-hopping communication therewith. For telephony, speech is digitally encoded. Digital data is transmitted in packets using successive bursts at different frequencies separated by intervals of silence. Each slave station has its own frequency-hopping pattern independent of the patterns of the other slave stations but sharing a common pool of available frequencies. The master stations are capable of generating any of the slave station patterns instantly. The master stations broadcast network time information for synchronization purpose, and the slave station patterns are determined by a combination of a slave station identification number and network time.
U.S. Pat. No. 4,532,636 to Wilkinson discloses radio communications receivers for use on frequency hopping communications networks in which the received signal in each hop period is analyzed and assigned a quality value. If more than one signal is present during the hop period, it is determined that more than one network has changed to the same frequency. Similarly, if the received signal is out of synchronism, it is determined that more than one network has changed to the same frequency. When more than one network has changed to the same frequency, the received signal is not output by the receiver but is replaced by an earlier (or later) received signal.
U.S. Pat. No. 5,038,399 to Bruckert discloses a radio frequency communication system employing channelization, such as a cellular TDMA system, and having a plurality of reuse channel levels, such as multiple frequency reuse patterns, each level having at least one associated reuse channel, a method and device comprising: determining relative interference for a reuse channel of a first reuse level in relation to relative interference for a reuse channel of at least a second reuse level resulting in a reuse level gradient and assigning the subscriber unit to at least one reuse level in response to the reuse level gradient.
U.S. Pat. No. 5,079,768 to Flammer discloses a frequency-hopping packet communication system without a master clock or master control unit which bases use of a receiver's frequency hopping timing and identification to control communication. A frequency-hopping band plan, involving the number of channels and the pseudo-random pattern of frequency change and nominal timing of changes, is universally known to each node in the network. Frequency-hopping is implemented by the division of communication slots and the accumulation of slots into epochs, wherein each epoch equals the total number of available slots (number of channels times the number of time frames per channel). A transmitting node tracks the preestablished frequency-hopping pattern for its target receiver based on previously-acquired information. The transmission node identifies a receiver node and a current frequency channel of such receiver node. The transmission node then checks the frequency channel to determine if available (e.g., not in use and within an acceptable noise margin). If unavailable, the transmission node delays transmission to the identified node to a later slot. During the delay, the transmission node identifies another receiver node and a corresponding current frequency channel. The steps of identifying a receiver node and checking the corresponding current frequency channel are repeated until a node having an available frequency channel is identified. The transmission node then sends a packet to the selected receiver node at a frequency and for a duration defined according to the current slot. Such transmission node tracks the changing frequency of the selected receiver node to maintain frequency synchronization.
U.S. Pat. No. 5,123,029 to Bantz et al, which is assigned to the assignee of this invention discloses a hybrid of controlled access and random access schemes using frequency hopping spread spectrum communication techniques, and which is implemented in an indoor digital data radio communication system between mobile stations and a computer system. A hop in the frequency hopping spread spectrum communication system is subdivided into two intervals so that different media-access protocols can be used in each interval. The protocol uses a centralized control scheme in one interval and a decentralized scheme in the other, and the intervals may be varied depending on the load of the system. U.S. Pat. No. 5,123,029 is incorporated herein by reference.
According to the present invention, control algorithms are derived for automated management of Frequency-Hopping operations in multiple cell radio networks. Specific problems solved include: 1) The assignment of frequency hopping patterns to multiple cells within an autonomous multicell network. 2) Assignment methods by which multiple autonomous, collocated networks can choose Frequency Hopping patterns and adapt their behavior such that the probability of intercell interference is minimized. These methods enable independent network operation without the need for any explicit coordination between networks. 3) Revision of Frequency Hopping patterns to minimize the impact of interference.